Abstract:
The impact of the Fe (III)-reducing bacteria Shewanella alga on the solid phase partitioning of dissolved Sr2+ was investigated in a series of experiments using live cells, dead cells (heat-treated at 80°C) and isolated cell envelope fractions. The synthetic hydrous ferric oxide (HFO) used in the experiments was prepared in the laboratory by titration of FeCl3 with NaOH. The presence of dissolved Fe (II) was observed only in response to the reductive dissolution of HFO by S. alga in experiments conducted with live cells, nor was the production of dissolved Fe (II) by the live cells inhibited by 1 mM Sr2+. pH increased in each of the bacterial systems (live, dead, cell envelope) as well as in the abiotic control (HFO, no bacteria) over the time course of the experiment (5 days) due presumably to a pCO2 drawdown of the culture medium in response to equilibration with the N2 atmosphere of the anaerobic chamber used in the investigation. In the presence of the live Fe (III)-reducing bacteria, the pH increase was sufficient to bring about supersaturation with respect to siderite after approximately 2 days. Solid phase Sr2+ capture was greatest in the live cell systems (60%) followed by dead cell and cell envelope treatments (40%), and least in the abiotic control (10%). The greater percentage solid phase capture of Sr2+ in the presence of the live cells is due to both sorption and precipitation processes occurring in this experimental system. These results show that non-viable S. alga cells and cell envelopes can sorb significantly greater quantities of Sr2+ compared to HFO alone, and that siderite precipitation in live S. alga cultures enhances the solid phase partitioning of Sr2+.